1. Field of the Invention
The present invention relates to an oscillator, such as a voltage-controlled oscillator or the like, for use in optical communication devices, the oscillator having a phase shifter and a power distributor in a dielectric substrate made up of a plurality of dielectric layers.
2. Description of the Related Art
As electronic devices are becoming smaller and thinner, there are also demands for smaller and thinner oscillators for use in optical communication devices.
Conventional oscillators comprise chip components mounted on a glass epoxy substrate. It has been difficult to reduce the size of the conventional oscillators because the mounted chip components take up a large installation area on the glass epoxy substrate.
For the purpose of reducing size, an oscillator having an organic multilayer substrate such as a glass epoxy substrate or the like includes interconnections and striplines disposed between the layers of the organic multilayer substrate, and individual chip components mounted on the surface layer of the organic multilayer substrate. Since the size of the organic multilayer substrate is determined by the layout of the mounted chip components, the line width of the interconnections and small-size chip components are used for thereby reducing the installation area of the organic multilayer substrate.
An oscillator employing a dielectric substrate made of alumina having a low dielectric constant or the like can have a reduced number of individual chip components mounted on the surface layer, further reducing the substrate area because passive components fabricated according to the thick-film forming technology and interconnections can be placed on inner layers of the dielectric substrate. For details, reference should be made to Japanese Laid-Open Patent Publication No. 2002-57525.
There are instances where the number of components is reduced by providing a distributed-constant circuit, rather than a lumped-constant circuit, in a dielectric substrate (see, for example, Japanese Laid-Open Patent Publication No. 4-207512, Japanese Laid-Open Patent Publication No. 2001-313501, and Japanese Laid-Open Patent Publication No. 2003-110360). There are also disclosed directional couplers whose size is effectively reduced by two spiral striplines disposed in confronting relation to each other with a dielectric layer sandwiched therebetween for changing a lumped-constant circuit to a distributed-constant circuit (see, for example, Japanese Laid-Open Patent Publication No. 51-78671 and Japanese Laid-Open Patent Publication No. 5-243820).
Heretofore, most size-reducing attempts are directed to changing a lumped-constant circuit to a distributed-constant circuit and specifying the configuration of the distributed-constant circuit. However, suggestions have not been made with respect to the layout of circuit components in a dielectric substrate. If the layout of circuit components is taken into consideration, then even an oscillator with a lumped-constant circuit can sufficiently be reduced in size. Furthermore, if the lumped-constant circuit is changed to a distributed-constant circuit, then the number of components can be reduced and the oscillator can be further reduced in size, thereby making the electronic device incorporating the oscillator smaller.